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Thought I might add something regarding the comparative accuracy of the
various sight reduction methods spoken of here from time to time.

Over the years, I have experimented under all conditions at sea with most
methods, at least through HO 249 - specifically this is meant to include
the Longitude Time Sight, Marc St. Hillaire, Ageton, Dreisenstok,
Martelli, several British Admiralty methods, HO 214, and HO 249 - and
never found any significant discrepancy as respects positions found, with
the possible exception of HO 249 in the use of which "rounding off"
errors seemed to tend to multiply and result in more than the usual
number of "cocked hats". As a matter of convenience, especially in
cramped small vessel navigation, I favored Dreisenstok (HO 208) over most
other methods and could match speed of calculation, as well as accuracy,
with most any other method - for pre-computation of altitude and azimuth,
I found HO 249 a handy accessory tool.

I became at one time enamored with (and still am) Martelli's Tables which
constitute one of the first short tabular methods for solution of the
Longitude Time Sight, although in recalculating, I have found several
errors or misprints in my copy. These tables are simple and easy to use,
and with a little manipulation can serve for intercept calculation.
Unfortunately they do not provide for the computation of azimuth, for
which other tables or formulae must be employed.

As respects the age old discussion of utilizing a DR position, as opposed
to an assumed position, in any intercept method, there never seemed to be
any significant or practical difference in positions established by
whatever method was used. This of course does not refer to utilization of
the Time Sight solely for longitude, in which case an accurate Latitude
must be employed - the more so as the body moves out of the prime
vertical toward the meridian.

Someday I will share with you my experience with Lunar Distance
observations at sea, which date back to the 1940's before the apparent
current renewal of interest.

Regards.

                                        Henry

   

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